Hippocampus

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Hippocampus

Both clinical neuropsychological studies and animal experiments involving damage to the hippocampal formation indicate that this structure plays a fundamental role in at least the initial establishment of long-term associative memory; however, the exact role of the hippocampus in associative memory, and the physiological and computational mechanisms by which this role is accomplished, remain subjects of intense study and debate. Although by no means proven, evidence favors the hypothesis that the hippocampus acts as a simple interim repository for memories of certain kinds of events, and that other (neocortical) circuitry draws on this repository during a process known as memory consolidation (e.g., Zola-Morgan and Squire, 1990). The following is a brief overview of some current ideas about how the unique circuitry of the hippocampal formation might enable rapid associative memory, and why such an interim repository might be necessary.

Specific events are generally represented in the nervous system as distributed patterns of activity within rather large populations of cells, and rarely by the activity of single cells. The activity pattern may be thought of as a vector, that is, a list of ones and zeros, indicating which neurons are firing and which are silent, or as a list of positive real numbers indicating the firing rates of the neurons over some short interval. Associative recall, by its most general definition, is the ability of the brain to reconstruct the vector corresponding to a stored event when presented with a vector that is missing some of the original information, has been corrupted somehow by noise, or merely bears some significant resemblance to the original. …